This proposal includes investigation of the molecular pathology of three inborn errors, characterization of "new" and rare metabolic disorders, evaluation of clinical effects of early treatment and therapeutic regimens in several relatively frequent metabolic disorders, monitoring the health of women with inborn errors during pregnancy and evaluation of the outcome of their offspring. 1) In fumarase deficiency, a disorder of the citric acid cycle associated with severe neurologic impairment, the structural gene for human fumarase will be characterized and the mutations in deficient patients analyzed. In homocystinuria (HCS) due to cystathionine beta-synthase deficiency, DNA mutations and genetic heterogeneity will be investigated in patients with both the B6 responsive and nonresponsive forms and in those from varied ethnic backgrounds. In ornithine transcarbamylase deficiency, molecular analysis will focus on patients with very atypical clinical presentations. 2) Two unknown sulfur-containing amino acids detected in the urine of two unrelated neurologically impaired patients are probably derivatives of methionine, homocyst(e)ine or cyst(e)ine. These metabolites will be identified using analytical and chromatographic techniques. 3) Large excretion of D-2-hydroxy-glutarate was detected in an infant who developed encephalopathy at age 3 months. The metabolism of this unusual organic acid in humans is virtually unknown. Extrapolation from experimental animal data suggests that a dehydrogenase for the family of D-2-hydroxy acids or specific for D-2-hydroxyglutarate exists in humans and may be defective in this patient. Our proposed studies will establish the activity of these enzymes in human tissue for the first time and characterize any defect in this disease. 4) The effectiveness of long-term betaine treatment in HCS patients will be evaluated particularly in the prevention of vascular disease, osteoporosis, and ocular lens dislocation. 5) Long-term outcome of early treatment in patients with urea cycle disorders and maple syrup urine disease will continue. Evaluation of offspring outcome in maternal PKU and other inborn errors in relation to severity of maternal disease and effects of treatment will be performed. In women with disorders characterized by episodic metabolic crisis, the stress of pregnancy on metabolic homeostasis will be monitored. The goals of this work are to understand the relationship between the biochemical, molecular, pathophysiologic and clinical aspects in these disorders so that effective therapies can be developed.